In fiber-optic sensors, it is often advantageous to conduct the radiation going to the sensor head and the radiation returning from the sensor head through one and the same fiber. This corresponds to the duplex method (bidirectional transmission) known from communications technology wherein information is transmitted through one fiber in both directions.
German Utility Model DE-U1 80 04 633and U.S. patent application Ser. No.688,098, filed on Apr. 19, 1991, now U.S. Pat. No. 5,077,813, discloses a configuration suitable for fiber-optic sensors for coupling in the radiation of a radiation source into a fiber and for guiding the returning radiation to a receiver. In this configuration, a reference beam path is provided in an arrangement identified as an optical switch. With this reference beam path, the radiation of the radiation source can be conducted directly to the receiver.
A disadvantage of this known arrangement is that reliance must be placed on mechanically movable parts when switching over to the reference beam path and when switching back to the measuring beam path. If a second receiver is provided for the reference beam path then the disadvantage must be assumed that this second receiver and, when appropriate, the amplifier corresponding thereto does not precisely have the same characteristics as the first receiver and as a consequence of the foregoing, the measurements are imprecise.